Backlight unit and liquid-crystal display device using the same

ABSTRACT

An edge-light type backlight unit reduces the color unevenness on the display screen caused by the arrangement of point-shaped light sources (e.g., LEDs) in a point-shaped light source unit comprising a set of point-shaped light sources aligned. The backlight unit includes at least one point-shaped light source unit having point-shaped light sources arranged in a single direction in a predetermined order, the light sources emitting monochromatic light of different colors. The unit further comprises a first optical filter for limiting or controlling transmission of the monochromatic light emitted from one of the light sources disposed at one end of the light source unit, and a second optical filter for limiting or controlling transmission of the monochromatic light emitted from another of the light sources disposed at the other end thereof. The first and second filters are selectively formed on a first or second light guide plate or a diffusing plate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a backlight unit and a Liquid-CrystalDisplay (LCD) device and more particularly, to a backlight unit withpoint-shaped light sources such as Light-Emitting Diodes (LEDs), whichis preferably applicable to LCD devices, and a LCD device using thebacklight unit.

2. Description of the Related Art

In recent years, the LCD device has been extensively used ashigh-resolution displays. Generally, the LCD device comprises asubstrate on which switching elements such as Thin-Film Transistors(TFTs) are arranged, which will be termed a “TFT substrate” below; anopposite substrate on which a color filter, a black matrix or the likeare formed; and a liquid-crystal layer intervening between the TFTsubstrate and the opposite substrate. By changing the alignmentdirection of the liquid-crystal molecules in the liquid-crystal layerwith the electric field generated between the pixel electrodes on theTFT substrate and the common electrode on the opposite substrate orbetween the common and pixel electrodes on the TFT substrate, the amountof transmitting light in the respective pixels is controlled to displayimages on the screen of the LCD device. The assembly comprising the TFTsubstrate, the opposite substrate, and the intervening liquid-crystallayer between these two substrates is termed the liquid-crystal displaypanel or LCD panel.

With the transmissive and semi-transmissive type LCD devices, abacklight unit is incorporated as a planer light source, because theliquid crystal per se does not emit light. The light emitted from onesurface of the backlight unit, i.e., backlight, is designed in such away as to be irradiated to the LCD panel. The backlight unit is dividedinto two types, the “direct type” and the “edge-light type”. With the“direct type” backlight unit, linear or point-shaped light sources arearranged directly underneath the LCD panel with a predetermined layout.On the other hand, with the “edge-light type”, a linear light source orsources or point-shaped light sources is/are arranged along an edge oredges of a light guide plate disposed right under the LCD panel.

With the conventional backlight units, a cold-cathode fluorescent lamphas been popularly used as a linear light source. However, acold-cathode fluorescent lamp contains mercury (Hg) and thus, there is aproblem that it gives bad effects to the environment largely. Moreover,since a cold-cathode fluorescent lamp necessitates high voltage foremitting light, there is another problem that it is likely to generatenoises. Accordingly, recently, there has been a growth in the use ofLEDs as a point-shaped light source.

Where LEDs are used as the light source instead of cold-cathodefluorescent lamps, obtainable luminance by a white LED for emittingwhite light or by a set of three LEDs for respectively emitting red,green, and blue monochromatic light is insufficient. Therefore, it ispopular that a plurality of white LEDs or a set of plural red, green,and blue LEDs is linearly arranged to form a linear light source. Suchthe combination of LEDs as explained here is termed a “LED unit” below.This is because there is an advantage that the LED unit can be treatedin designing in a similar way to the cold-cathode fluorescent lamp andtherefore, the know-how and the like obtained for the cold-cathodefluorescent lamp may be applied to the LED unit.

With the direct type backlight unit, however, the obtainable luminanceon the diffusing plate provided for diffusing the output light emittedfrom the light source varies dependent upon the location. Specifically,the obtainable luminance on the diffusing plate in the regionimmediately above the LED unit is higher than that in the remainingregion. Thus, the luminance distribution on the display screen is likelyto be uneven. Since this leads to unevenness in color and/or luminance,there is the need to adjust the said luminance distribution.

Moreover, with the LED unit formed by combining LEDs each emitting red,green, or blue monochromatic light, there is the need to mix the red,green, and blue light to generate white light. (Such the need is trivialfor the LED unit formed by aligning white LEDs alone.) Therefore, it isessential to increase the distance between the LEDs and the diffusingplate to some extent. This means that the backlight unit and the LCDdevice incorporating the same will be large-sized.

To solve these two problems, i.e., “the non-uniformity of the luminancedistribution” and “the enlargement in size”, conventionally, variousimprovements have been made. Examples of these improvements are shown inFIGS. 1A and 1B. Both of the prior-art backlight units shown in FIGS. 1Aand 1B are of the direct type, which are disclosed in the patentdocument 1 (Japanese Non-Examined Patent Publication No. 2004-311353published in 2004). (See claim 1, paragraphs 0010-0026 and 0046-0049,and FIGS. 1-3 and 11.)

With the prior-art backlight unit of FIG. 1A, plate-shaped reflectorsare respectively formed on the inner bottom face 101a and the inner sideface of a housing 101. The reflector formed on the bottom face 101a istermed the first reflector 102. The opening 101b of the housing 101,which is opposite to the bottom face 101a, is closed or blocked by adiffusion plate 103 for transmitting and diffusing the light.

As the point-shaped light sources 104, a plurality of LEDs each emittingred (R), green (G), or blue (B) monochromatic light is combinedtogether. The LEDs 104 are mounted on each of the point-shaped lightsource substrates 105 along its longitudinal direction, which isperpendicular to the paper. Here, the count of the substrates 105 isthree, which are aligned at predetermined intervals. The arrangement ofthe LEDs 104 mounted on each of the substrates 105 is made by repetitionof a specific order, for example, G, B, G, R, G, and B. Each substrate105 is fixed on the outside of the bottom face 101a of the housing 101,and the LEDs 104 mounted on the said substrate 105 are exposed from thebottom face 101a to the inside of the housing 101 through its bottomwall.

Rectangular plate-shaped second reflectors 106, the count of which isthree, are provided in the housing 101 in such a way as to be superposedon the respective substrates 105. Each of the second reflectors 106 hasa reflective surface 106a opposite to the corresponding first reflector102. The reverse of the reflective surface 106a is a regular reflectionsurface 106b. The second reflectors 106 are fixed on the inner side faceof the housing 101 in such a way as to be approximately parallel to thefirst reflectors 102. A gap is formed between the side face of thehousing 101 and the second reflector 106 adjacent thereto, and anothergap is formed between the adjoining second reflectors 106. Thus, thelight emitted from the point-shaped light sources 104 can reach the sideof the diffusing plate 103 by way of these gaps.

With the prior-art backlight unit having the above-describedconfiguration of FIG. 1A, the R, G, and B monochromatic light beamsemitted from the LEDs or point-shaped light sources 104 are directlyreflected by the first reflector 102 and then, reflected by thereflective surfaces 106a of the second reflectors 106. Alternately,these light beams are reflected by the reflective surfaces 106a of thesecond reflectors 106, and reflected by the first reflector 102 andthereafter, reflected again by the reflective surfaces 106a. In thisway, these monochromatic light beams are repeatedly reflected andpropagated between the first reflector 102 and the second reflectors 106and as a result, they are mixed together and uniformized to white light.The white light thus generated will reach the diffusing plate 103 by wayof the gaps between the side face of the housing 101 and the secondreflectors 106 and the gaps between the adjoining second reflectors 106.

The light incident on the diffusing plate 103 is divided into acomponent that penetrates through the inside of the diffusing plate 103and another component that is reflected by the particles in thediffusing plate 103 toward the side of the point-shaped light sources104. The reflected component of the said light is reflected by the firstreflector 102 or the regular reflection surfaces 106b of the secondreflectors 106 and is incident again on the plate 103. The outgoinglight from the diffusing plate 103 will radiate from its surface in alldirections uniformly.

As explained above, the R, G, and B monochromatic light emitted from theLEDs 104 are repeatedly reflected and propagated in the space betweenthe first reflector 102 and the second reflectors 106 and therefore,sufficient distances for mixture to white light are obtained. As aresult, the color unevenness of the LCD device can be prevented fromoccurring without enlargement in size.

In addition, conventionally, the luminance in the region immediatelyabove the LEDs (i.e., the point-shaped light sources) 104 is higher thanthat in the remaining or surrounding region thereof and thus, theluminance distribution on the display screen is likely to be uneven.Unlike this, with the prior-art backlight unit of FIG. 1A, because thesecond reflectors 106 are provided between the LEDs 104 and the firstreflector 102, such the luminance unevenness can be suppressed.

The prior-art backlight unit shown in FIG. 1B has the same configurationas the prior-art backlight unit shown in FIG. 1A except that patternedlight-shielding layers 110a are selectively printed on a surface (i.e.,the inner surface in FIG. 1B) of the diffusing plate 103. Each of thelight-shielding layers 110a has a diffuse reflection function ofincident light. Each of the light-shielding layers 110a is located inthe area to which the light is irradiated through the gaps between theside face of the housing 101 and the second reflector 106 adjacentthereto and the gaps formed between the adjoining second reflectors 106.The light-shielding layers 110a are formed by vacuum evaporation or silkprinting of aluminum (Al). The size, density and gradation of the inkdots and/or the deposited patterns constituting the layers 110a areadjusted to realize uniform luminance distribution.

With the prior-art backlight unit of FIG. 1B, the light passing throughthe gaps between the side face of the housing 101 and the secondreflector 106 adjacent thereto and the gaps between the adjoining secondreflectors 106 reaches the light-shielding layers 110a and isdiffuse-reflected by the layers 110a and then, further diffused in thehousing 101. Thus, the luminance unevenness and color unevenness aremore likely to be suppressed than the prior-art backlight unit of FIG.1A.

Moreover, although not shown, still another prior-art direct typebacklight unit is disclosed in the patent document 2 (JapaneseNon-Examined Patent Publication No. 2005-117023 published in 2005). (Seeclaim 1, paragraphs 0129-0131 and 0143-0147, and FIGS. 17 and 24.) Thisbacklight unit comprises a similar structure to the patternedlight-shielding layers 110a of the prior-art backlight unit of FIG. 1B.

With the structure shown in FIGS. 17 and 24 of the patent document 2, aplurality of LED units are arranged at intervals on the inner bottomsurface of a housing. Each of the LED units comprises LEDs alignedregularly. A diffusing plate is fixed at the mouth of the housinglocated on the opposite side to the bottom surface. A diffusing lightguide plate is provided between the bottom surface and the diffusingplate. Patterned light-controlling dots are formed on a surface of thediffusing light guide plate. Each of the light-controlling dots isplaced in a one-on-one relationship with an opposing one of the LEDs.These dots are formed by printing with ink.

Each of the light-controlling dots reflects the incident light due tothe reflection property of the ink. At the same time, each of the dotsdiffuse-reflects the incident light efficiently due to the shieldingproperty of the light-shielding agent added to the ink and the diffusionproperty of the diffusing agent added thereto. Accordingly, generationof high-luminance regions termed the lamp images is prevented, in otherwords, luminance unevenness is suppressed, which results in equalizedluminance.

Moreover, because of the light-controlling dots, the light penetratingthrough the diffusing light guide plate exhibits high color mixingproperty. Therefore, the color unevenness of the resultant light issuppressed significantly.

With any of the above-described prior-art direct type backlight units,luminance unevenness and color unevenness can be suppressed withoutenlargement in size. However, as long as a set of LEDs (i.e.,point-shaped light sources) emitting red, green, and blue monochromaticlight is used in combination, it is inevitable that color unevenness isleft on the display screen in accordance with the placement order of theLEDs in the set. For example, if a red LED emitting red light is placedat one end of the LED unit, color mixture is difficult to occur withrespect to the red LED. This is because a green or blue LED is notplaced adjacent to the said red LED on one side thereof. Therefore, thecorresponding position on the display screen to the said red LEDcontains some redness compared with the other positions.

The above problem of color unevenness for the direct type backlight unitwill occur in the edge-light type backlight unit. In particular, thisphenomenon is more likely to occur if the edge-light type backlight unitcomprises a single LED unit formed by a set of red, green and blue LEDsaligned in a single direction. This is because the light emitted fromthe respective LEDs of plural LED units is unable to be mixed together.

Furthermore, since all the above-described prior-art backlight units areof the direct type, the patterned light-shielding layers and thepatterned light-controlling dots used therein are not easily applied tothe edge-light type backlight units.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide anedge-light type backlight unit that reduces the color unevenness on thedisplay screen caused by the arrangement of point-shaped light sourcesin a point-shaped light source unit comprising a set of the alignedpoint-shaped light sources, and a LCD device using the backlight unit.

The above object together with others not specifically mentioned willbecome clear to those skilled in the art from the following description.

According to a first aspect of the present invention, an edge-light typebacklight unit is provided, which comprises:

at least one point-shaped light source unit having point-shaped lightsources arranged in a single direction in a predetermined order, thelight sources emitting monochromatic light of different colors;

a first light guide plate, which has a light incident surface and alight exiting surface, for receiving monochrome light emitted from therespective light sources of the light source unit at the light incidentsurface and guiding the said light to the light exiting surface;

a reflector for reflecting the light exiting from the light exitingsurface of the first light guide plate;

a second light guide plate, which has a light incident surface and alight exiting surface, for receiving the light reflected by thereflector at the light incident surface of the second light guide plateand guiding the said light to the light exiting surface of the secondlight guide plate;

a diffusing plate for receiving the light exiting from the light exitingsurface of the second light guide plate, diffusing the said light, andemitting the said light diffused;

a first optical filter for limiting or controlling transmission of themonochromatic light emitted from one of the light sources disposed atone end of the light source unit; and

a second optical filter for limiting or controlling transmission of themonochromatic light emitted from another of the light sources disposedat the other end of the light source unit;

wherein the first optical filter and the second optical filter areselectively formed on one of the first light guide plate, the secondlight guide plate, and the diffusing plate.

With the backlight unit according to the first aspect of the presentinvention, at least one point-shaped light source unit havingpoint-shaped light sources arranged in a single direction in apredetermined order is provided, where the point-shaped light sourcesemit monochromatic light of different colors. Thus, if the first opticalfilter and the second optical filter are not provided, it is inevitablethat color unevenness is left on the display screen in accordance withthe placement order of the point-shaped light sources in the lightsource unit.

However, the first optical filter and the second optical filter areselectively formed on one of the first light guide plate, the secondlight guide plate, and the diffusing plate. The first optical filterlimits or controls transmission of the monochromatic light emitted fromone of the light sources disposed at one end of the light source unit.The second optical filter limits or controls transmission of themonochromatic light emitted from another of the light sources disposedat the other end of the light source unit.

Therefore, the effect given by the monochromatic light emitted from thelight sources disposed at each end of the light source unit is limitedor controlled effectively.

In this way, with the backlight unit according to the first aspect ofthe present invention, by selectively providing the first and secondoptical filters on one of the first light guide plate, the second lightguide plate, and the diffusing plate, penetration or transmission of thecolored light causing the color unevenness (which is due to thearrangement or sequence of the point-shaped light sources) is limited orcontrolled, thereby decreasing the said color unevenness. As a result,the color unevenness on the display screen can be reduced effectivelywith a very simple structure.

In a preferred embodiment of the backlight unit according to the firstaspect of the present invention, the first and second optical filtersare located on the light exiting surface of the first light guide plate.In this embodiment, it is preferred that the first and second opticalfilters are respectively located at or near two ends of the lightexiting surface of the first light guide plate, respectively.

In another preferred embodiment of the backlight unit according to thefirst aspect of the present invention, the first and second opticalfilters are located on the light incident surface of the second lightguide plate. In this embodiment, it is preferred that the first andsecond optical filters are respectively located at or near two ends ofthe light incident surface of the second light guide plate.

In still another preferred embodiment of the backlight unit according tothe first aspect of the present invention, the first and second opticalfilters are located on the light exiting surface of the second lightguide plate. In this embodiment, it is preferred that the first andsecond optical filters are respectively located at or near two ends ofthe light exiting surface of the second light guide plate.

In a further preferred embodiment of the backlight unit according to thefirst aspect of the present invention, the first and second opticalfilters are located on one surface of the diffusing plate. In thisembodiment, it is preferred that the first and second optical filtersare respectively located at or near two ends of the surface of thediffusing plate.

In a still further preferred embodiment of the backlight unit accordingto the first aspect of the present invention, the count of the lightsource unit is unity. In this embodiment, the advantage of the inventionis exhibited remarkably. Specifically, if the count of the point-shapedlight source unit is two or more, the color deviation caused by themonochromatic light from the point-shaped light sources located at eachend of the respective light source units can be relaxed bydifferentiating the arrangement or sequence of the point-shaped lightsources in the light source units and placing them adjacently. However,if the count of the point-shaped light source unit is unity, such themeasure is impossible to be realized. The effect by the said colordeviation will appear conspicuously. With the backlight unit accordingto the first aspect of the present invention, however, the said colordeviation can be effectively relaxed even if the count of thepoint-shaped light source unit is unity.

According to a second aspect of the present invention, a LCD device isprovided, which comprises:

the backlight device according to the first aspect of the invention; and

a liquid-crystal display panel to which the light emitted from thebacklight unit is to be irradiated.

With the LCD device according to the second aspect of the presentinvention, since the backlight unit according to the first aspect of theinvention is included, the color unevenness on the display screen can beeffectively reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the present invention may be readily carried into effect,it will now be described with reference to the accompanying drawings.

FIG. 1A is a schematic partial cross-sectional view showing theconfiguration of a prior-art direct type backlight unit.

FIG. 1B is a schematic partial cross-sectional view showing theconfiguration of another prior-art direct type backlight unit.

FIG. 2 is a schematic perspective exploded view showing theconfiguration of the main part of an edge-light type backlight unitaccording to a first embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view showing the configuration ofthe main part of the backlight unit according to the first embodiment ofFIG. 2.

FIG. 4 is a schematic perspective exploded view showing theconfiguration of the main part of an edge-light type backlight unitaccording to a second embodiment of the present invention.

FIG. 5 is a schematic perspective exploded view showing theconfiguration of the main part of an edge-light type backlight unitaccording to a third embodiment of the present invention.

FIG. 6 is a schematic perspective exploded view showing theconfiguration of the main part of an edge-light type backlight unitaccording to a fourth embodiment of the present invention.

FIG. 7 is a schematic cross-sectional view showing the configuration ofthe main part of a LCD device according to a fifth embodiment of thepresent invention, which comprises the backlight unit according to thefirst embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described indetail below while referring to the drawings attached.

First Embodiment

FIGS. 2 and 3 schematically show the configuration of a backlight unit 1according to a first embodiment of the present invention.

As shown in FIGS. 2 and 3, the backlight unit 1 according to the firstembodiment, which is of the edge-light type, comprises a LED unit 11into which a plurality of LEDs 11b are incorporated as point-shapedlight sources. The unit 1 further comprises a rectangular first lightguide plate 12, an approximately hemicylindrical reflector 13, arectangular second light guide plate 14, and a rectangular diffusingplate 15. These optical members are fixed by a housing or frame (notshown) to have the configuration shown in FIG. 3.

Each of the LEDs 11b of the LED unit 11 emits red, green, or bluemonochromatic light. These LEDs 11b are aligned and fixed on a base 11aat equal intervals in a predetermined order or sequence. The base 11a isformed by a belt-shaped rigid plate. For example, the LEDs 11b arealigned from one end of the base 11a (i.e., the LED row) to the otherend thereof in the order of G, B, G, R, G, B, . . . , R. This means thatthe LED 11a emitting green (G) light is located at one end of the base11a (at the left end in FIG. 2), and the LED 11a emitting red (R) lightis located at the other end of the base 11a (at the right end in FIG.2).

The LED unit 11 is fixed near the light incident surface 12a of thefirst light guide plate 12 to have a predetermined gap therebetween. Thelight incident surface (or the light incident end face) 12a is formed onone of the two longer side faces of the plate 12. The LED unit 11 isextended parallel to the light incident surface 12a. Thus, the LEDs 11bare aligned along the light incident surface 12a in the above-describedorder. The red, green or blue monochromatic light emitted from each ofthe LEDs 11b enters the inside of the first light guide plate 12 by wayof the light incident surface 12a. Then, the red, green and blue lightfrom the LEDs 11b propagates through the inside of the first light guideplate 12, and exits from the light exiting surface (or the light exitingend face) 12b of the plate 12 to the outside. The light exiting surface12b is formed on the other of the two longer side faces of the plate 12,which is opposite to the light incident surface 12a.

Appropriate processing has been applied to the other surfaces of thefirst light guide plate 12 than the light incident and exiting surfaces12a and 12b by a known method in such a way that the light propagatingin the plate 12 is reflected. Thus, the light that has entered theinside of the plate 12 through the light incident surface 12a isreflected repeatedly due to total internal reflection on thereflection-processed surfaces of the plate 12, and propagates toward thelight exiting surface 12b, outgoing or exiting through the light exitingsurface 12b.

The second light guide plate 14 and the first light guide plate 12 arearranged and fixed in parallel to each other to have a minute gaptherebetween. In FIG. 3, the second light guide plate 14 is located overthe first light guide plate 12. The first and second light guide plates12 and 14 are located in such a way that the light exiting surface 12bof the first light guide plate 12 and the light incident surface (or thelight incident end face) 14a of the second light guide plate 14 aresuperposed (aligned) on each other. The light incident surface 14a ofthe second light guide plate 14 is formed on one of the two longer sidefaces thereof. Since the second light guide plate 14 is larger than thefirst light guide plate 12, the first light guide plate 12 is entirelycovered with the second light guide plate 14.

The reflector 13 is fixed near the light exiting surface 12b of thefirst light guide plate 12 and the light incident surface 14a of thesecond light guide plate 14 in such a way as to extend along these twosurfaces 12b and 14a. As shown in FIG. 3, an approximatelyhemicylindrical reflective surface 13a of the reflector 13, which islocated inside the reflector 13, is opposed to the surfaces faces 12band 14a. The reflective surface 13a reflects the light emitted from thelight exiting surface 12b of the first light guide plate 12 and make thesaid light enter the second light guide plate 14 by way of its lightincident surface 14a.

Similar to the first light guide plate 12, appropriate processing hasbeen applied to the other surfaces of the second light guide plate 14than the light incident surface 14a and the planar light exiting surface14b by a known method in such a way that the light propagating in theplate 14 is reflected. Thus, the light that has entered the inside ofthe plate 14 through the light incident surface 14a is reflectedrepeatedly due to total internal reflection on the reflection-processedsurfaces of the plate 14, and propagates in the plate 14, outgoing fromthe light exiting surface 14b toward the diffusing plate 15 (upward inFIG. 3).

The diffusing plate 15, which is located on the opposite side to thefirst light guide plate 12 with respect to the second light guide plate14, is parallel to the second light guide plate 14 to be apart from theplate 14 at a predetermined distance. One surface of the diffusing plate15 is opposed to the light exiting surface 14b of the second light guideplate 14. The light emitted from the light exiting surface 14b of theplate 14 to enter the diffusing plate 15 is diffused in the plate 15 andthen, is irradiated to a LCD panel (not shown) in the form of collimatedlight.

On the light incident surface 14a of the second light guide plate 14, asclearly shown in FIG. 2, an optical filter 20a and an optical filter 20bare selectively formed to limit or control the color unevennessoccurring on the display screen of a LCD device. The filter 20a islocated at or near one end (the left-side end in FIG. 3) of the lightincident surface 14a, and the filter 20b is located at or near the otherend (the right-side end in FIG. 3) thereof. The filter 20a limits orcontrols the transmission of the light radiated from the LED 11b at ornear one end (the left-side end in FIG. 2) of the LED unit 11. On theother hand, the filter 20b limits or controls the transmission of thelight radiated from the LED 11b at or near the other end (i.e., theright-side end in FIG. 2) of the LED unit 11. Each of the filters 20aand 20b has a predetermined width along the light incident surface 14a.The width of the filter 20a may be the same as or different from that ofthe filter 20b. The filters 20a and 20b are apart from each other at apredetermined distance.

The reason why the optical filters 20a and 20b are provided on the lightincident surface 14a of the second light guide plate 14 is as follows.Specifically, the backlight unit 1 according to the first embodimentcomprises the LED unit 11 having the LEDs 11b arranged in a singledirection (i.e., along the elongated base 11a in FIG. 2) in thepredetermined order or sequence, where each of the LEDs 11b emitsmonochromatic light of red, green or blue. The green LED 11b is locatedat one end (i.e., the left-side end in FIG. 2) of the LED unit 11 andthe red LED 11b is located at the other end (i.e., the right-side end)thereof. Therefore, green and red colors are likely to be excessive orstronger in the neighborhoods of each end (i.e., the left- andright-side ends) of the LED unit 11, respectively. In other words, colordeviation will take place in these neighborhoods. As a result, colorunevenness will occur on the display screen due to the said colordeviation. However, with the backlight unit 1 of the first embodiment,the filters 20a and 20b operate to cancel the color deviation and thus,the color unevenness on the screen is restrained or eliminated.

The formation method of the filters 20a and 20b is not limited. Anymethod may be used for this purpose. For example, an ink that limits orcontrols the transmission of light of a desired color may be printed onthe light incident surface 14a of the second light guide plate 14 toform a predetermined pattern or patterns. Alternately, a patternedcolored sheet or sheets or the like that limits or controls thetransmission of light of a desired color may be adhered on the lightincident surface 14a, or a material for the colored sheet(s) may beselectively coated on the surface 14a. Here, each of the filters 20a and20b is formed by a set of dots. However, the shape or pattern of thefilters 20a and 20b is not limited to this. The filters 20a and 20b mayhave any other shape or pattern such as linear (or, strip-shaped) andplanar ones. In short, it is sufficient for the filters 20a and 20b thatthe transmission of light of a desired color is limited or controlled inthe regions where the filter 20a and 20b are formed, respectively.

To find what color of light is to be limited or controlled and how muchthe light needs to be limited or controlled, for example, the followingmethod is preferably used. Specifically, all the LEDs 11b of the LEDunit 11 are activated by driving the LED unit 11 in the state where theoptical filters 20a and 20b are not formed, thereby emitting light fromall the LEDs 11b. Then, the light radiated from the diffusing plate 15(i.e., backlight) due to the light from the LEDs 11b is irradiated tothe LCD panel. During that time, color unevenness occurring on thedisplay screen is examined or researched. As a result, it is known whatcolor of light is excessive and how much the color exceeds in theneighborhood of each end of the screen. The color of light thus foundought to reflect the color of light emitted from the LED 11b located ateach end of the LED unit 11. Thereafter, an appropriatelight-transmission limiting or controlling material that brings thetransmission amount of light of the excessive color near zero as much aspossible is selectively applied to each of the required regions on thelight incident surface 14a of the second light guide plate 14, therebyforming the optical filters 20a and 20b.

Next, the operation of the backlight unit 1 having the above-describedconfiguration is explained below.

When the power of the backlight unit 1 is turned on, red, green, or bluemonochromatic light is emitted from each of the LEDs 11b of the LED unit11 toward the light incident surface 12a of the first light guide plate12. The red, green and blue monochromatic light thus emitted enters theinside of the first light guide plate 12 by way of the light incidentsurface 12a. Then, the said light is reflected repeatedly in the plate12 due to total internal reflection and propagates to the light exitingsurface 12b, exiting from the said face 12b. The said red, green andblue light is somewhat mixed together in the plate 12; however, such thecolor mixture is insufficient and the effect by the arrangement (order)of the LEDs 11b remains. Specifically, green color is somewhat excessiveor stronger in the neighborhood of one end (i.e., the left-side end inFIG. 2) of the light exiting surface 12 and at the same time, red coloris somewhat excessive or stronger in the neighborhood of the other end(i.e., the right-side end in FIG. 2) thereof. In the remaining region(in the central part in FIG. 2) other than the neighborhoods of thesetwo ends of the light exiting surface 12, the said red, green and bluelight is considerably mixed together and as a result, it will be nearwhite light.

The light emitted from the light exiting surface 12 of the first lightguide plate 12 is reflected by the reflective surface 13a of thereflector 13 to enter the inside of the second light guide plate 14through the light incident surface 14a thereof. At that time, due to theoptical filter 20a that limits or controls the transmission of greenlight and the optical filter 20b that limits or controls thetransmission of red light, which are formed respectively at or near thetwo ends of the light incident surface 14a, the amounts of thetransmitted green and red light are reduced. This means that the amountsof the green and red light incident on the surface 14a are respectivelydecreased by the filters 20a and 20b in the neighborhoods of the twoends of the surface 14a. Accordingly, in the second light guide plate14, the color deviation of the outgoing or exiting light from the firstlight guide plate 12 is limited or controlled.

The light that has entered the inside of the second light guide plate 14is reflected repeatedly due to total internal reflection and propagatesin the inside of the plate 14. During that time, the red, green and bluelight is further mixed together to be an approximately uniform whitelight. Thereafter, the approximately uniform white light thus generatedexits upward from the planar light exiting surface 14b of the plate 14toward the diffusing plate 15, as shown in FIG. 3. With the backlightunit 1 according to the first embodiment of the invention shown in FIGS.2 and 3, as explained above, the LED unit 11 with the LEDs 11b emittingred, green and blue light is provided. The green LED 11b is located ator near one end (i.e., the left-side end in FIG. 2) of the LED unit 11,and the red LED 11b is located at or near the other end (i.e., theright-side end in FIG. 2) thereof. All the LEDs 11b of the unit 11 arealigned along the light incident surface 12a of the first light guideplate 12. For this reason, if the optical filters 20a and 20b are notprovided, green color will be excessive or stronger in one side of thedisplay screen and at the same time, red color will be excessive orstronger in the other side thereof compared with the remaining region(i.e., the central part) of the screen in accordance with the placementorder of the LEDs 11b in the LED unit 11. As a result, color unevennessor color deviation will occur on the screen.

However, the backlight unit 1 comprises the filter 20a that limits orcontrols the transmission of the green light at or near the left-sideend of the light incident surface 14a of the second light guide plate 14and the filter 20b that limits or controls the transmission of the redlight at or near the right-side end thereof. Therefore, the effect bythe green light emitted from the green LED 11b at the left-side end ofthe LED unit 11 and the red light emitted from the red LED 11b at theright-side end thereof can be limited or restrained effectively with avery simple structure. Accordingly, the color unevenness on the displayscreen can be reduced.

Moreover, since the backlight unit 1 is of the edge type, the size ofthe unit 1 is not enlarged for color mixture, which is unlike the directtype backlight unit.

In addition, by combining the backlight unit 1 according to the firstembodiment with a known LCD panel, a LCD device having less colorunevenness can be fabricated.

Second Embodiment

FIG. 4 schematically shows the configuration of a backlight unit 1Aaccording to a second embodiment of the present invention.

The backlight unit 1A of the second embodiment has the sameconfiguration as the backlight unit 1 of the first embodiment of FIGS. 2and 3 except that optical filters 21a and 21b are selectively formed onthe light exiting surface 12b of the first light guide plate 12, insteadof the optical filters 20a and 20b formed on the light incident surface14a of the second light guide plate 14 in the first embodiment.Therefore, explanation about the same configuration as the backlightunit 1 according to the first embodiment is omitted here by attachingthe same reference numerals as those of the first embodiment to the sameor corresponding elements.

In this way, like the backlight unit 1 according to the firstembodiment, the backlight unit 1A according to the second embodimentcomprises the LED unit 11 with the LEDs 11b emitting red, green and bluelight is provided. The green LED 11b is located at the left-side end ofthe LED unit 11 and the red LED 11b is located at the right-side endthereof. All the LEDs 11b of the unit 11 are aligned along the lightincident surface 12a of the first light guide plate 12. For this reason,if the filters 21a and 21b are not provided, green and red colors willbe excessive or stronger in or near each side of the display screencompared with the remaining region (i.e., the central part) of thescreen in accordance with the placement order of the LEDs 11b in theunit 11. As a result, color unevenness or color deviation will occur onthe screen.

However, with the backlight unit 1A, the filter 21a that limits orcontrols the transmission of the green light is selectively formed at ornear the left-side end of the light exiting surface 12b of the firstlight guide plate 12 while the filter 21b that limits or controls thetransmission of the red light is selectively formed at or near theright-side end thereof. Each of the filters 21a and 21b has apredetermined width along the light exiting surface 12b. Therefore, theeffect by the green and red light emitted from the green and red LEDs11b at each end of the LED unit 11 can be limited or restrainedeffectively. Accordingly, the color unevenness on the display screen canbe reduced with a very simple structure.

In addition, by combining the backlight unit 1A according to the secondembodiment with a known LCD panel, a LCD device having less colorunevenness can be fabricated.

Third Embodiment

FIG. 5 schematically shows the configuration of a backlight unit 1Baccording to a third embodiment of the present invention.

The backlight unit 1B has the same configuration as the backlight unit 1according to the first embodiment of FIGS. 2 and 3 except that opticalfilters 22a and 22b are selectively formed on the planar light exitingsurface 14b of the second light guide plate 14, instead of the opticalfilters 20a and 20b formed on the light incident surface 14a of thesecond light guide plate 14 in the first embodiment. Therefore,explanation about the same configuration as the backlight unit 1Baccording to the third embodiment is omitted here by attaching the samereference numerals as those of the first embodiment to the same orcorresponding elements.

With the backlight unit 1B, as shown in FIG. 5, the filter 22a thatlimits or controls the transmission of the green light is selectivelyformed at or near the left-side end of the light exiting surface 14b ofthe second light guide plate 14, and the filter 22b that limits orcontrols the transmission of the red light is selectively formed at ornear the right-side end thereof. The filter 22a is extended along theleft-side end (i.e., the left-side shorter edge) of the surface 14b tohave a predetermined width. The filter 22b is extended along theright-side end (i.e., the right-side shorter edge) of the surface 14b tohave a predetermined width. The filters 22a and 22b are apart from eachother at a predetermined distance. Therefore, the effect by the greenand red light emitted from the green and red LEDs 11b at each end of theLED unit 11 can be limited or restrained effectively. Accordingly, thecolor unevenness on the display screen can be reduced with a very simplestructure.

In addition, by combining the backlight unit 1B according to the thirdembodiment with a known LCD panel, a LCD device having less colorunevenness can be fabricated.

Fourth Embodiment

FIG. 6 schematically shows the configuration of a backlight unit 1Caccording to a fourth embodiment of the present invention.

The backlight unit 1C has the same configuration as the backlight unit 1according to the first embodiment of FIGS. 2 and 3 except that opticalfilters 23a and 23b are selectively formed on one surface (i.e., anincident or exiting surface) of the diffusing plate 15 instead of theoptical filters 20a and 20b formed on the light incident surface 14a ofthe second light guide plate 14 in the first embodiment. Therefore,explanation about the same configuration as the backlight unit 1according to the first embodiment is omitted here by attaching the samereference numerals as those of the first embodiment to the same orcorresponding elements.

With the backlight unit 1C, as shown in FIG. 6, the filter 23a thatlimits or controls the transmission of the green light is selectivelyformed at or near the left-side end of the surface of the diffusingplate 15, and the filter 23b that limits or controls the transmission ofthe red light is selectively formed at the right-side end thereof. Thefilter 23a is extended along the left-side end (i.e., the left-sideshorter edge) of the surface of the plate 15 to have a predeterminedwidth. The filter 23b is extended along the right-side end (i.e., theright-side shorter edge) of the surface of the plate 15 to have apredetermined width. The filters 23a and 23b are apart from each otherat a predetermined distance. Therefore, the effect by the green and redlight emitted from the green and red LEDs 11b at each end of the LEDunit 11 can be limited or restrained effectively. Accordingly, the colorunevenness on the display screen can be reduced with a very simplestructure.

In addition, by combining the backlight unit 1C according to the fourthembodiment with a known LCD panel, a LCD device having less colorunevenness can be fabricated.

Fifth Embodiment

FIG. 7 schematically shows the configuration of a LCD device 50according to a fifth embodiment of the present invention. The LCD device50 comprises a LCD panel 90 and the above-described backlight unit 1according to the first embodiment.

The LCD panel 90 may have any one of the known configurations. Here, asshown in FIG. 7, the panel 90 comprises a TFT substrate 60, a CF (colorfilter) or opposite substrate 70, and a liquid-crystal layer 80sandwiched by these two substrates 60 and 70.

The TFT substrate 60 comprises a glass plate 61, a TFT array 62 formedon the inner surface of the plate 61, an alignment layer 63 formed onthe TFT array 62, and a polarizer 64 formed on the outer surface of theplate 61. The TFT array 62 includes pixel electrodes (not shown)arranged in a matrix array.

The CF substrate 70 comprises a glass plate 71, a color filter 72 formedon the inner surface of the plate 71, an opposite or common electrode 73formed on the color filter 72, an alignment layer 74 formed on theopposite electrode 73, and a polarizer 75 formed on the outer surface ofthe plate 71.

Voltages are applied across the pixel electrodes in the TFT array 62 andthe opposite electrode 73 with respect to the respective pixels. Byswitching the applied voltages using the TFTs in the TFT array 62,desired images are displayed on the screen.

With the LCD device 50 according to the fifth embodiment, since thebacklight unit 1 according to the first embodiment is used, the colorunevenness on the display screen can be effectively reduced.

The backlight unit 1 according to the first embodiment may be replacedwith the backlight unit 1A, 1B, or 1C according to the second, third, orfourth embodiment described above.

VARIATIONS

The above-described first to fifth embodiments are preferred examples ofthe present invention. Therefore, it is needless to say that the presentinvention is not limited to these embodiments. Any other modification isapplicable to the embodiments.

For example, in the above-described embodiments of the invention, theoptical filters are selectively formed on the light exiting surface ofthe first light guide plate, the light incident surface or the lightexiting surface of the second light guide plate, or the surface of thediffusing plate. However, two or more of these embodiments may becombined together according to the necessity. Specifically, the opticalfilters may be formed on the light incident surface of the second lightguide plate and one surface of the diffusing plate, respectively.Alternately, the optical filters may be formed on the light exitingsurface of the first light guide plate and one surface of the diffusingplate, respectively. Any other combination is applicable to theinvention.

Moreover, in the above-described embodiments of the invention, theoptical filters are selectively formed at or near each end of the lightexiting surface of the first light guide plate, the light incident orexiting surface of the second light guide plate, or one surface of thediffusing plate. However, the invention is not limited to this.According to the color unevenness or deviation appearing in any area orareas other than the ends of the display screen, the optical filter orfilters may be selectively formed on the light exiting surface of thefirst light guide plate, the light incident or exiting surface of thesecond light guide plate, or the diffusing plate.

In addition, a single LED unit is used for the backlight unit in theabove-described embodiments of the invention. However, two or more LEDunits may be used in combination for the backlight unit.

Although parallel flat light guide plates are used for the first andsecond light guide plates in the above-described embodiments of theinvention, any other type of the light guide plate, such as awedge-shaped light guide plate, may be used for this purpose.

While the preferred forms of the present invention have been described,it is to be understood that modifications will be apparent to thoseskilled in the art without departing from the spirit of the invention.The scope of the present invention, therefore, is to be determinedsolely by the following claims.

What is claimed is:
 1. A backlight unit comprising: at least onepoint-shaped light source unit having point-shaped light sourcesarranged in a single direction in a predetermined order, the lightsources emitting monochromatic light of different colors; a first lightguide plate, which has a light incident surface and a light exitingsurface, for receiving monochrome light emitted from respective lightsources of the light source unit at the light incident surface andguiding said light to the light exiting surface; a reflector forreflecting the light exiting from the light exiting surface of the firstlight guide plate; a second light guide plate, which has a lightincident surface and a light exiting surface, for receiving the lightreflected by the reflector at the light incident surface of the secondlight guide plate and guiding said light to the light exiting surface ofthe second light guide plate; a diffusing plate for receiving the lightexiting from the light exiting surface of the second light guide plate,diffusing said light, and emitting said light diffused; a first opticalfilter for limiting or controlling transmission of the monochromaticlight emitted from one of the light sources disposed at one end of thelight source unit; and a second optical filter for limiting orcontrolling transmission of the monochromatic light emitted from anotherof the light sources disposed at the other end of the light source unit,wherein the first optical filter and the second optical filter areselectively formed on one of the first light guide plate, the secondlight guide plate, and the diffusing plate, and wherein a base of saidpoint-shaped light source unit is parallel to said light incidentsurface of the first light guide plate.
 2. A backlight unit comprising:at least one point-shaped light source unit having point-shaped lightsources arranged in a single direction in a predetermined order, thelight sources emitting monochromatic light of different colors; a firstlight guide plate, which has a light incident surface and a lightexiting surface, for receiving monochrome light emitted from respectivelight sources of the light source unit at the light incident surface andguiding said light to the light exiting surface; a reflector forreflecting the light exiting from the light exiting surface of the firstlight guide plate; a second light guide plate, which has a lightincident surface and a light exiting surface, for receiving the lightreflected by the reflector at the light incident surface of the secondlight guide plate and guiding said light to the light exiting surface ofthe second light guide plate; a diffusing plate for receiving the lightexiting from the light exiting surface of the second light guide plate,diffusing said light, and emitting said light diffused; a first opticalfilter for limiting or controlling transmission of the monochromaticlight emitted from one of the light sources disposed at one end of thelight source unit; and a second optical filter for limiting orcontrolling transmission of the monochromatic light emitted from anotherof the light sources disposed at the other end of the light source unit,wherein the first optical filter and the second optical filter areselectively formed on one of the first light guide plate, the secondlight guide plate, and the diffusing plate, and wherein the firstoptical filter and the second optical filter are located on the lightexiting surface of the first light guide plate.
 3. The backlight unitaccording to claim 2, wherein the first optical filter and the secondoptical filter are respectively located at or near two ends of the lightexiting surface of the first light guide plate, respectively.
 4. Abacklight unit comprising: at least one point-shaped light source unithaving point-shaped light sources arranged in a single direction in apredetermined order, the light sources emitting monochromatic light ofdifferent colors; a first light guide plate, which has a light incidentsurface and a light exiting surface, for receiving monochrome lightemitted from respective light sources of the light source unit at thelight incident surface and guiding said light to the light exitingsurface; a reflector for reflecting the light exiting from the lightexiting surface of the first light guide plate; a second light guideplate, which has a light incident surface and a light exiting surface,for receiving the light reflected by the reflector at the light incidentsurface of the second light guide plate and guiding said light to thelight exiting surface of the second light guide plate; a diffusing platefor receiving the light exiting from the light exiting surface of thesecond light guide plate, diffusing said light, and emitting said lightdiffused; a first optical filter for limiting or controllingtransmission of the monochromatic light emitted from one of the lightsources disposed at one end of the light source unit; and a secondoptical filter for limiting or controlling transmission of themonochromatic light emitted from another of the light sources disposedat the other end of the light source unit, wherein the first opticalfilter and the second optical filter are selectively formed on one ofthe first light guide plate, the second light guide plate, and thediffusing plate, and wherein the first optical filter and the secondoptical filter are located on the light incident surface of the secondlight guide plate.
 5. The backlight unit according to claim 4, whereinthe first optical filter and the second optical filter are respectivelylocated at or near two ends of the light incident surface of the secondlight guide plate.
 6. The backlight unit according to claim 1, whereinthe first optical filter and the second optical filter are located onthe light exiting surface of the second light guide plate.
 7. Thebacklight unit according to claim 6, wherein the first optical filterand the second optical filter are respectively located at or near twoends of the light exiting surface of the second light guide plate. 8.The backlight unit according to claim 7, wherein the first opticalfilter and the second optical filter extend along the ends of the lightexiting surface of the second light guide plate, respectively.
 9. Thebacklight unit according to claim 1, wherein the first optical filterand the second optical filter are located on one surface of thediffusing plate.
 10. The backlight unit according to claim 9, whereinthe first optical filter and the second optical filter are respectivelylocated at or near two ends of the surface of the diffusing plate. 11.The backlight unit according to claim 10, wherein the first opticalfilter and the second optical filter extend along the ends of thesurface of the diffusing plate, respectively.
 12. The backlight unitaccording to claim 1, wherein the light source unit comprises a singleLight Emitting Diode (LCD) unit.
 13. A liquid-crystal display devicecomprising: the backlight unit according to claim 1; and aliquid-crystal display panel to which the light emitted from thebacklight unit is to be irradiated.
 14. The backlight unit according toclaim 1, wherein the backlight unit comprises an edge-light type unit.15. The backlight unit according to claim 1, wherein the first opticalfilter and the second optical filter are selectively formed on one ofthe first light guide plate or said light incident surface of the secondlight guide plate.
 16. The backlight unit according to claim 1, whereinsaid point-shaped light sources comprise a different light color at eachside of the point-shaped light source unit.
 17. The backlight unitaccording to claim 13, wherein the first optical filter and the secondoptical filter are located on the light exiting surface of the firstlight guide plate.
 18. The backlight unit according to claim 13, whereinthe first optical filter and the second optical filter are selectivelyformed on one of the first light guide plate or said light incidentsurface of the second light guide plate.
 19. A backlight unitcomprising: at least one point-shaped light source unit havingpoint-shaped light sources arranged in a single direction in apredetermined order, the light sources emitting monochromatic light ofdifferent colors; a first light guide plate, which has a light incidentsurface and a light exiting surface, for receiving monochrome lightemitted from respective light sources of the light source unit at thelight incident surface and guiding said light to the light exitingsurface; a reflector for reflecting the light exiting from the lightexiting surface of the first light guide plate; a second light guideplate, which has a light incident surface and a light exiting surface,for receiving the light reflected by the reflector at the light incidentsurface of the second light guide plate and guiding said light to thelight exiting surface of the second light guide plate; a diffusing platefor receiving the light exiting from the light exiting surface of thesecond light guide plate, diffusing said light, and emitting said lightdiffused; a first optical filter for limiting or controllingtransmission of the monochromatic light emitted from one of the lightsources disposed at one end of the light source unit; and a secondoptical filter for limiting or controlling transmission of themonochromatic light emitted from another of the light sources disposedat the other end of the light source unit, wherein the first opticalfilter and the second optical filter are selectively formed on one ofthe first light guide plate or said light incident surface of the secondlight guide plate.
 20. The backlight unit according to claim 19, whereinthe backlight unit comprises an edge-light type unit, and wherein a baseof said point-shaped light source unit is parallel to said lightincident surface of the first light guide plate.
 21. A backlight unitcomprising: a first light guide plate; a second light guide plate; adiffusing plate; a first optical filter for controlling transmission ofmonochromatic light emitted from one of a set of point-shaped lightsources disposed at one end of a point-shaped light source unit; and asecond optical filter for controlling transmission of monochromaticlight emitted from another of the set of point-shaped light sourcesdisposed at another end of the point-shaped light source unit, whereinthe first optical filter and the second optical filter are selectivelyformed on one of the first light guide plate, the second light guideplate, or the diffusing plate, wherein a base of the point-shaped lightsource unit is substantially parallel to a light incident surface of thefirst light guide plate.
 22. The backlight unit of claim 21, wherein thefirst optical filter and the second optical filter are respectivelylocated on a light exiting surface of the second light guide plate. 23.The backlight unit of claim 22, wherein the first optical filter and thesecond optical filter are respectively located at or near two ends ofthe light exiting surface of the second light guide plate.
 24. Thebacklight unit of claim 23, wherein the first optical filter and thesecond optical filter respectively extend along the two ends of thelight exiting surface of the second light guide plate.
 25. The backlightunit of claim 21, wherein the first optical filter and the secondoptical filter are located on a surface of the diffusing plate.
 26. Thebacklight unit of claim 25, wherein the first optical filter and thesecond optical filter are respectively located at or near two ends ofthe surface of the diffusing plate.
 27. The backlight unit of claim 26,wherein the first optical filter and the second optical filter extendrespectively along the two ends of the surface of the diffusing plate.28. The backlight unit of claim 21, wherein the point-shaped lightsource unit comprises a light emitting diode unit.
 29. The backlightunit of claim 21, further comprising a liquid-crystal display panelconfigured to receive irradiated light from the set of point-shapedlight sources.
 30. The backlight unit of claim 21, wherein the backlightunit comprises an edge-type unit wherein the point-shaped light sourceunit is arranged along an edge of the first light guide plate.
 31. Thebacklight unit of claim 21, wherein the first optical filter and thesecond optical filter are selectively formed on one of the first lightguide plate or a light incident surface of the second light guide plate.32. The backlight unit of claim 21, wherein the first optical filter andthe second optical filter are located on a light exiting surface of thefirst light guide plate.
 33. The backlight unit of claim 32, wherein thefirst optical filter and the second optical filter are respectivelylocated at or near two ends of the light exiting surface of the firstlight guide plate.
 34. The backlight unit of claim 21, wherein the setof point-shaped light sources comprises a different light color atrespective sides of the point-shaped light source unit.
 35. A backlightunit comprising: a first light guide plate; a first optical filterconfigured to limit or control transmission of monochromatic lightemitted from one of a set of light sources disposed at one end of alight source unit; and a second optical filter configured to limit orcontrol transmission of monochromatic light emitted from another of theset of light sources disposed at another end of the light source unit,wherein the first optical filter and the second optical filter arelocated on a light exiting surface of the first light guide plate. 36.The backlight unit of claim 35, wherein the first optical filter and thesecond optical filter are respectively located at or near two ends ofthe light exiting surface of the first light guide plate.
 37. Thebacklight unit of claim 35, wherein the light source unit comprises alight emitting diode unit.
 38. The backlight unit of claim 35, furthercomprising a liquid-crystal display panel configured to receive lightemitted from the set of point-shaped light sources.
 39. The backlightunit of claim 35, wherein the backlight unit comprises an edge-type unitwherein the light source unit is arranged alone, an edge of the firstlight guide plate.
 40. The backlight unit of claim 35, wherein the setof light sources comprising a set of point-shaped light sources.
 41. Abacklight unit comprising: a first light guide plate; a second lightguide plate; a first optical filter configured to control transmissionof monochromatic light emitted from one of a set of light sourcesdisposed at one end of a light source unit; and a second optical filterconfigured to control transmission of monochromatic light emitted fromanother of the set of light sources disposed at another end of the lightsource unit, wherein the first optical filter and the second opticalfilter are located on a light incident surface of the second light guideplate.
 42. The backlight unit of claim 41, wherein the first opticalfilter and the second optical filter are respectively located at or neartwo ends of the light incident surface of the second light guide plate.43. The backlight unit of claim 41, wherein the light source unitcomprises a light emitting diode unit.
 44. The backlight unit of claim41, further comprising a liquid-crystal display panel to which lightemitted from the set of point-shaped light sources is to be irradiated.45. The backlight unit of claim 41, wherein the backlight unit comprisesan edge-type unit wherein the light source unit is arranged along anedge of the first light guide plate.
 46. The backlight unit of claim 41,wherein the set of light sources comprises a set of point-shaped lightsources.
 47. A backlight unit comprising: a first light guide plate; asecond light guide plate; a first optical filter configured to limittransmission of monochromatic light emitted from one of a set of lightsources disposed at one end of a light source unit; and a second opticalfilter configured to limit transmission of monochromatic light emittedfrom another of the set of light sources disposed at another end of thelight source unit, wherein the first optical filter and the secondoptical filter are selectively formed on one of the first light guideplate or a light incident surface of the second light guide plate. 48.The backlight unit of claim 47, wherein the backlight unit comprises anedge-type unit, and wherein a base of the light source unit issubstantially parallel to a light incident surface of the first lightguide plate.
 49. The backlight unit of claim 47, wherein the lightsource unit comprises a single light emitting diode unit.
 50. Thebacklight unit of claim 47, further comprising a liquid-crystal displaypanel to which light emitted from the set of light sources is to beirradiated.
 51. The backlight unit of claim 47, wherein the backlightunit comprises an edge-type unit wherein the light source unit isarranged along an edge of the first light guide plate.
 52. The backlightunit of claim 47, wherein the first optical filter and the secondoptical filter are located on a light exiting surface of the first lightguide plate.
 53. The backlight unit of claim 52, wherein the firstoptical filter and the second optical filter are respectively located ator near two ends of the light exiting surface of the first light guideplate.
 54. The backlight unit of claim 47, wherein the set of lightsources comprises a different light color at respective sides of thelight source unit.
 55. A method comprising: receiving, at a lightincident surface of a first light guide plate, first light emitted froma first light source disposed on a first end of a light source unithaving a base that is substantially parallel to the light incidentsurface of the first light guide plate; receiving, at the light incidentsurface of the first light guide plate, second light emitted from asecond light source disposed on a second end of the light source unit;guiding, by a second light guide plate, the first light and the secondlight to a diffusing plate; controlling transmission of the first lightby a first optical filter formed on one of the first light guide plate,the second light guide plate, or the diffusing plate; and controllingtransmission of the second light by a second optical filter formed onone of the first light guide plate, the second light guide plate, or thediffusing plate.
 56. The method of claim 55, wherein: the controllingtransmission of the first light includes controlling transmission of thefirst light by the first optical filter located on a light exitingsurface of the second light guide plate; and the controllingtransmission of the second light includes controlling transmission ofthe second light by the second optical filter located on the lightexiting surface of the second light guide plate.
 57. The method of claim55, wherein: the controlling transmission of the first light includescontrolling transmission of the first light by the first optical filterlocated on a first end of a surface of the diffusing plate; and thecontrolling transmission of the second light includes controllingtransmission of the second light by the second optical filter located ona second end of the surface of the diffusing plate.
 58. The method ofclaim 55, wherein the receiving the first light and the receiving thesecond light includes receiving the first light and the second lightfrom a light emitting diode unit.
 59. The method of claim 55, wherein:the controlling transmission of the first light includes controllingtransmission of the first light by the first optical filter located on afirst end of a light exiting surface of the first light guide plate; andthe controlling transmission of the second light includes controllingtransmission of the second light by the second optical filter located ona second end of the light exiting surface of the first light guideplate.
 60. The method of claim 55, wherein: the controlling transmissionof the first light includes controlling transmission of the first lightby the first optical filter located on a light incident surface of thesecond light guide plate; and the controlling transmission of the secondlight includes controlling transmission of the second light by thesecond optical filter located on the light incident surface of thesecond light guide plate.
 61. The method of claim 55, further comprisingguiding the first light and the second light to a light exiting surfaceof the first light guide plate.
 62. The method of claim 61, furthercomprising reflecting the first light and the second light from thelight exiting surface of the first light guide plate to a light incidentsurface of the second light guide plate.
 63. The method of claim 59,wherein the receiving first light and the receiving the second lightincludes receiving the first light and the second light emitted from afirst point-shaped light source and a second point-shaped light source,respectively.
 64. A system comprising: means for receiving first lightand second light from a first end and a second end, respectively, of alight source unit having a base that is substantially parallel to alight incident surface of the means for receiving the first light andthe second light; means for guiding the first light and the second lightto a diffusing plate; means for limiting or controlling transmission ofthe first light; and means for limiting or controlling transmission ofthe second light, wherein the means for limiting or controllingtransmission of the first light and the means for limiting orcontrolling transmission of the second light are formed on one of themeans for receiving the first light and the second light, the means forguiding, or the diffusing plate.